Acute myelogenous leukemia/acute myeloid leukemia (AML) is a myeloproliferative disease that is characterized by an elevated count of immature myeloid blasts in bone marrow and peripheral blood. It is the most common type of leukemia in adults and accounts for approximately 25% of all leukemias in the Western World. The incidence is highest in the US, Australia and Western Europe, with about 3.8 cases per 100,000 in the US and Europe (Deschler and Lubbert, 2006; Showel and Levis, 2014).
AML is a disease of the elderly: The incidence for adults over 60 years is 15 cases per 100,000 (Showel and Levis, 2014). Patients newly diagnosed with AML have a median age of 67 years (American Cancer Society, 2015). Males have a slightly higher risk for developing AML in most countries (Deschler and Lubbert, 2006).
AML has the lowest survival rate of all leukemias (Deschler and Lubbert, 2006). The 5-year overall survival (OS) in patients older than 75 is less than 10% with no improvement over the last 30 years. The 5-year OS for patients aged 25 to 39 has improved from less than 10% to 50% (Showel and Levis, 2014). The mortality rate for males is higher than for females. AML mortality is greater in whites than in blacks (Deschler and Lubbert, 2006).
AML is diagnosed when at least 20% (World Health Organization (WHO) classification) or at least 30% (French-American-British (FAB) classification) blasts of the myeloid lineage are present in bone marrow or blood. Diagnosis is done on blood or bone marrow samples. Tests include a complete blood count and microscopic exams, cytochemistry, immunohistochemistry, flow cytometry, reverse transcriptase polymerase chain reaction (RT-PCR) and fluorescence in-situ hybridization (FISH) (National Cancer Institute, 2015).
Symptoms for AML are often unspecific and include weight loss, loss of appetite, fatigue, fever, headaches and sleepiness. Risk factors for developing AML include smoking, male gender, exposure to benzene, chemotherapeutical treatment with alkylating agents or topoisomerase II inhibitors and radiation exposure (National Cancer Institute, 2015).
As AML is a very heterogenous disease there is no unique classification system. The WHO classifies AML according to morphology, cytogenetics, molecular genetics and immunologic markers. The FAB system classifies AML using morphology as determined by the degree of differentiation and the extend of cell maturation. Depending on the above-named criteria the following AML subtypes exist according to WHO and FAB (National Cancer Institute, 2015):
WHO:
Percentage ofClassificationDescriptionAMLAML withAML with t(8;21)(q22;q22) (AML/ETO) 5-12%characteristicAML with inv(16)(p13q22) or t(16;16)(p13;q22)10-12%genetic(CBF□/MYH11)abnormalitiesAPL: AML with t(15;17)(q22;q12) (PML/RARA and 5-8%variants)AML with 11q23 (MLL) abnormalities 5-6%AML withAML with FLT3 mutations (FLT3/ITD: 23%, FLT320-30%geneticpoint mutation: 7%)abnormalitiesAML with NPM1 mutationsin FLT3,AML with CEBPA mutationsNPM1,AML with t(9;11)(p22;q23) (MLLT3/MLL)CEBPA,AML with t(6;9)(p23;q34) (DEK/NUP214)MLLT3/MLL,AML with inv(3)(q21q26.2) or t(3;3)(q21;q26.2)DEK/NUP214,(RPN1/EVI1)RPN1/EVI1,AML with t(1;22)(p13;q13) (RBM15/MKL1)RBM15/MKL1AML withAML evolving from MDS or following MDS,multilineagevariants: AML with complex karyotype, AML withdysplasiadeletions/aberrations of/in the followingchromosomes: del(7q), del(5q), i(17q)7t(17p),del(13q), del(11q), del(12p)/t(12p), del(9q),idic(X)(q13), AML with translocations between thefollowing chromosomes: t(11;16)(q23;q13.3),t(3;21)(q26.2;q22.1), t(1;3)(p36.3;q21.1),t(2;11)(p21;q23), t(5;12)(q33;p12),t(5;7)(q33;q11.2), t(5;17)(q33;p13),t(5;10)(q33;q21), t(3;5)(q25;q34)AML andAlkylating agent-related AML and MDSMDS, therapyTopoisomerase II inhibitor-related AMLrelatedAML notAcute myeloblastic leukemia, minimally 5%otherwisedifferentiatedcategorizedAcute myeloblastic leukemia, without maturation10%Acute myeloblastic leukemia, with maturation30-45%Acute myelomonocytic leukemia (AMML)15-25%Acute monoblastic leukemia and acute monocytic 5-8%leukemiaAcute erythroid leukemias 5-6%Acute megakaryoblastic leukemia, variant: 3-5%transient myeloproliferative disorder in DownsyndromeAcute basophilic leukemia<1%Acute panmyelosis with myelofibrosisMyeloid sarcoma 2-8%AcuteAcute leukemia of undetermined lineageleukemias ofAcute leukemia with mixed phenotypeambiguousAcute leukemia with mixed lineagelineageHybrid acute leukemia
FAB:
ClassificationNameCytogeneticsM0acute myeloblastic leukemia,minimally differentiatedM1acute myeloblastic leukemia, withoutmaturationM2acute myeloblastic leukemia, witht(8;21)(q22;q22),maturationt(6;9)M3acute promyelocytic leukemia (APL)t(15;17)M4acute myelomonocytic leukemiainv(16)(p13q22),(AMML)del(16q)M4(Eo)acute myelomonocytic leukemia withinv(16), t(16;16)bone marrow eosinophiliaM5a andacute monoblastic leukemia and acutedel(11q), t(9;11),M5bmonocytic leukemiat(11;19)M6a andacute erythroid leukemiasM6bM7acute megakaryoblastic leukemiat(1;22)M8acute basophilic leukemia
AML treatment is divided into two phases: induction therapy and post-remission/“consolidation therapy”. Induction therapy is administered to induce remission and consists of combinational chemotherapy. Consolidation therapy consists of additional chemotherapy or hematopoietic cell transplantation (HCT) (Showel and Levis, 2014).
The most common chemotherapeutic drugs used to treat AML are cytarabine, daunorubicin, idarubicin and mitoxantrone followed by cladribine, fludarabine and diverse others. Azacitidine and decitabine (DNA hypomethylating agents) are now used for treatment of MDS/AML. Treatment for APL/AML M3 includes all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) (National Cancer Institute, 2015).
“Standard treatment” for AML is considered as “3+7”: 3 days of idarubicin or daunorubicin and 7 days of cytarabine, followed by several similar courses to achieve complete remission (CR) (Estey, 2014). The decision between standard therapy and clinical trial is based on the risk stratification. The European Leukemia Net (ELN) system distinguishes between the following prognostic groups:
Prognistic goupSubsets“Favorable”inv(16) or t(16;16); t(8;21); NK and NPM1+/FLT3 ITD−;NK and CEBPA+/+Intermediate-1NK and NPM1−/FLT3 ITD−; CEBPA+/−Intermediate-2Cytogenetic abnormalities not in “favorable” or“adverse” groups; FLT3 ITD+“Adverse”−5, −7, 5q-, abn 3q, 17p, 11q (other than 9;11), t(6;9),complex; insufficient metaphases for analysis
AML cases with intermediate-risk karyotype show either no karyotypic abnormalities or only one or two abnormalities not categorized as high- or low-risk.
FLT3 mutations are associated with an aggressive type of AML and a poor prognosis. They often occur together with NPM1 and DNMT3a (DNA methyltransferase 3A) mutations. NPM1 (nucleophosmin) mutations are a favorable prognostic indicator, if not found together with FLT3 mutations. CEPBA (CCAAT-enhancer-binding protein alpha/C/EBPα) mutations confer a survival advantage in the case of double or homozygous CEBPA mutations without wild-type expression. Altered methylation patterns in a variety of genes are caused by mutations in isocitrate dehydrogenase (IDH1 and IDH2) and DNMT3A. These mutations are associated with poor survival.
AML cases with favorable-risk karyotype consist of APL (acute promyelocytic leukemia) and CBF (core-binding factor) leukemias. APL cases are associated with the fusion of the myeloid transcription factor PML to the retinoic acid receptor subunit alpha (RARA). The PML/RARA translocation is a favorable prognostic mutation. CBF leukemia cases show translocations involving a subunit of CBF. In t(8;21) CBF alpha is fused to the ETO gene. In inv(16) CBF beta is fused to the smooth muscle myosin heavy chain. CBF translocations are very favorable prognostic mutations.
AML cases with unfavorable-risk karyotype are characterized by a complex karyotype including chromosomal aberrations such as translocations, unbalanced rearrangements and gains/losses of whole chromosomes. They are associated with a poor prognosis.
MDS/AML cases evolve from myelodysplastic syndromes and carry a worse prognosis than other AML sub-groups (Showel and Levis, 2014).
Besides the above-listed prognostic factors, additional molecular markers or marker combinations can be used to judge the prognosis in specific cytogenetic subsets:
TP53 mutations are the most unfavorable genetic alteration in AML. NPM1 mutated and FLT3 WT together with a mutation in IDH1 or IDH2 is seen as favorable. Unfavorable factors include a partial tandem duplication in the MLL gene, a mutated TET2 gene, FLT3 ITD+together with a mutation in DNMT3a and CEBPA, FLT3 ITD−together with a mutation in ASXL1 or PHF6, and CD25 expression (stem cell-like “signature” and poorer outcome). The presence of CKIT mutations converts the prognosis of patients with a favorable inv(16) or t(8;21) into a more intermediate range. SPARC is up-regulated in NK (normal karyotype) patients with unfavorable gene expression signature and down-regulated in association with the favorable NPM1 mutation. miR-155 over-expression conveys a poor prognosis in NK AML. Differentially methylated regions (DMRs) are prognostic when found in association with several genes (FLT3 mutation, NPM1 mutation). In this case, a lower expression is associated with a better prognosis (Estey, 2014).
Post-treatment information/information about minimal residual disease (MRD) should be included into following treatment decisions. These include the response to induction therapy, PCR of fusion transcripts, mutated genes and over-expressed genes to detect MRD and multi-parameter flow cytometry for observation of aberrant expression of surface antigens.
The following table combines AML prognostic groups and treatment recommendations:
Prognostic groupSubsetsInductionPost-remission“Favorable”inv(16) or t(16;16);3 + 7; considerara-C (6 doses × 2t(8;21); NK andFLAG-ida if age <60-65courses), possiblyNPM1+/FLT3 ITD−;preceded by 1NK and CEBPA+/+course FLAG-idaIntermediate-1/Int-1NK and NPM1−/3 + 7; consider (a)HCT from matchedFLT3 ITD−;FLAG-ida if age <60-65sibling donor (MSD)CEBPA+/−or (b) clinicalif risk NRM <20-25%;trialif not HCTcandidate FLAG-idathen ara-C orclinical trialIntermediate-2/Int-2Cytogenetic3 + 7; consider (a)HCT from MSD orabnormalities not inFLAG-ida if age <60-65URD if risk NRM <30%;“favorable” oror (b) clinicalotherwise as“adverse” groups;trial; clinical trialintermediate-1; ifFLT3 ITD+combiningFLT3+/FLT3 ITD+chemotherapy withconsider FLT3FLT3 inhibtor (e.g.inhibitor post HCTquizartinib,crenolanib)“Adverse”−5, −7, 5q-, abn 3q,Clinical trialHCT from MSD or17p, 11q (other thanURD if risk NRM <40%;9;11), t(6;9),consider post-complex;HCT trial; if notinsufficientHCT: candidatemetaphases forclinical trialanalysisNRM: non-relapse mortality after HCT
Treatment options for the prognostic groups favorable, intermediate-1 and possibly intermediate-2 include the “standard therapy” “3+7”, a combination of daunorubicin and cytarabine or idarubicin and cytarabine, or the administration of FLAG-ida, a combination of fludarabine, cytarabine, G-CSF and idarubicin. A third option is gemtuzumab ozogamicin (GO), which is a conjugate of an anti-CD33 monoclonal antibody and the cytotoxic agent calechiamicin. As CD33 is expressed in >90% of patients with AML, the use of GO in combination with 3+7 or FLAG-ida may lead to longer remissions and survival. Dasatinib is given in combination with 3+7 and then in combination with high-dose cytarabine in patients with CKIT mutations in inv(16) and t(8;21) AML (Estey, 2014).
Clinical trials are recommended for patients who belong to the prognostic groups unfavorable and intermediate-2. Treatment options include hypomethylating agents (HMAs) as azacitidine or decitabine, CPX-351, which is a liposomal formulation of daunorubicin and cytarabine in a 1:5 “optimal” molar ratio, and volasertib, which is an inhibitor of polo kinases. Volasertib is given in combination with LDAC (low-dose cytarabine). Several different FLT3 inhibitors can be administered in case of FLT3 mutations. These include sorafenib, which is given in combination with 3+7, quizartinib, a more selective inhibitor of FLT3 ITD that also inhibits CKIT, crenolanib, and midostaurin, an unselective FLT3 ITD inhibitor. Another treatment option is targeting CD33 with antibody-drug conjugates (anti-CD33+calechiamicin, SGN-CD33a, anti-CD33+actinium-225), bispecific antibodies (recognition of CD33+CD3 (AMG 330) or CD33+CD16) and chimeric antigen receptors (CARs) (Estey, 2014).
If possible, AML patients can undergo allogeneic hematopoietic cell transplantation (HCT). HCT in CR (complete remission) 1 should be performed if the expected reduction in risk of relapse is greater than the risk of HCT-related complications. HCT can also be performed in CR2 or with active disease, as some patients who relapse after not receiving HCT in CR1 can still be cured. Patients that are seen unfit for myeloablative (MA) intensity HCT (patients>70-75, frail younger patients) can undergo a reduced intensity HCT (RIC-HCT). Possible donors are MUDs (matched unrelated donors), haploidentical donors or cells from umbilical cords that exceed the number of MSD (matched sibling donors). One third of patients have a HLA-matched sibling and about 50% have a potential matched unrelated donor (MUD) (Estey, 2014).
Considering the severe side-effects and expense associated with treating cancer, there is a need to identify factors that can be used in the treatment of cancer in general and AML in particular. There is also a need to identify factors representing biomarkers for cancer in general and AML in particular, leading to better diagnosis of cancer, assessment of prognosis, and prediction of treatment success.
Immunotherapy of cancer represents an option of specific targeting of cancer cells while minimizing side effects. Cancer immunotherapy makes use of the existence of tumor associated antigens.
The current classification of tumor associated antigens (TAAs) comprises the following major groups:
a) Cancer-testis antigens: The first TAAs ever identified that can be recognized by T cells belong to this class, which was originally called cancer-testis (CT) antigens because of the expression of its members in histologically different human tumors and, among normal tissues, only in spermatocytes/spermatogonia of testis and, occasionally, in placenta.
Since the cells of testis do not express class I and II HLA molecules, these antigens cannot be recognized by T cells in normal tissues and can therefore be considered as immunologically tumor-specific. Well-known examples for CT antigens are the MAGE family members and NY-ESO-1.
b) Differentiation antigens: These TAAs are shared between tumors and the normal tissue from which the tumor arose. Most of the known differentiation antigens are found in melanomas and normal melanocytes. Many of these melanocyte lineage-related proteins are involved in biosynthesis of melanin and are therefore not tumor specific but nevertheless are widely used for cancer immunotherapy. Examples include, but are not limited to, tyrosinase and Melan-A/MART-1 for melanoma or PSA for prostate cancer.
c) Over-expressed TAAs: Genes encoding widely expressed TAAs have been detected in histologically different types of tumors as well as in many normal tissues, generally with lower expression levels. It is possible that many of the epitopes processed and potentially presented by normal tissues are below the threshold level for T-cell recognition, while their over-expression in tumor cells can trigger an anticancer response by breaking previously established tolerance. Prominent examples for this class of TAAs are Her-2/neu, survivin, telomerase, or WT1.
d) Tumor-specific antigens: These unique TAAs arise from mutations of normal genes (such as β-catenin, CDK4, etc.). Some of these molecular changes are associated with neoplastic transformation and/or progression. Tumor-specific antigens are generally able to induce strong immune responses without bearing the risk for autoimmune reactions against normal tissues. On the other hand, these TAAs are in most cases only relevant to the exact tumor on which they were identified and are usually not shared between many individual tumors. Tumor-specificity (or -association) of a peptide may also arise if the peptide originates from a tumor- (-associated) exon in case of proteins with tumor-specific (-associated) isoforms.
e) TAAs arising from abnormal post-translational modifications: Such TAAs may arise from proteins which are neither specific nor overexpressed in tumors but nevertheless become tumor associated by posttranslational processes primarily active in tumors. Examples for this class arise from altered glycosylation patterns leading to novel epitopes in tumors as for MUC1 or events like protein splicing during degradation which may or may not be tumor specific.
f) Oncoviral proteins: These TAAs are viral proteins that may play a critical role in the oncogenic process and, because they are foreign (not of human origin), they can evoke a T-cell response. Examples of such proteins are the human papilloma type 16 virus proteins, E6 and E7, which are expressed in cervical carcinoma.
T-cell based immunotherapy targets peptide epitopes derived from tumor-associated or tumor-specific proteins, which are presented by molecules of the major histocompatibility complex (MHC). The antigens that are recognized by the tumor specific T lymphocytes, that is, the epitopes thereof, can be molecules derived from all protein classes, such as enzymes, receptors, transcription factors, etc. which are expressed and, as compared to unaltered cells of the same origin, usually up-regulated in cells of the respective tumor.
There are two classes of MHC-molecules, MHC class I and MHC class II. MHC class I molecules are composed of an alpha heavy chain and beta-2-microglobulin, MHC class II molecules of an alpha and a beta chain. Their three-dimensional conformation results in a binding groove, which is used for non-covalent interaction with peptides.
MHC class I molecules can be found on most nucleated cells. They present peptides that result from proteolytic cleavage of predominantly endogenous proteins, defective ribosomal products (DRIPs) and larger peptides. However, peptides derived from endosomal compartments or exogenous sources are also frequently found on MHC class I molecules. This non-classical way of class I presentation is referred to as cross-presentation in the literature (Brossart and Bevan, 1997; Rock et al., 1990). MHC class II molecules can be found predominantly on professional antigen presenting cells (APCs), and primarily present peptides of exogenous or transmembrane proteins that are taken up by APCs e.g. during endocytosis, and are subsequently processed.
Complexes of peptide and MHC class I are recognized by CD8-positive T cells bearing the appropriate T-cell receptor (TCR), whereas complexes of peptide and MHC class II molecules are recognized by CD4-positive-helper-T cells bearing the appropriate TCR. It is well known that the TCR, the peptide and the MHC are thereby present in a stoichiometric amount of 1:1:1.
CD4-positive helper T cells play an important role in inducing and sustaining effective responses by CD8-positive cytotoxic T cells. The identification of CD4-positive T-cell epitopes derived from tumor associated antigens (TAA) is of great importance for the development of pharmaceutical products for triggering anti-tumor immune responses (Gnjatic et al., 2003). At the tumor site, T helper cells, support a cytotoxic T cell- (CTL-) friendly cytokine milieu (Mortara et al., 2006) and attract effector cells, e.g. CTLs, natural killer (NK) cells, macrophages, and granulocytes (Hwang et al., 2007).
In the absence of inflammation, expression of MHC class II molecules is mainly restricted to cells of the immune system, especially professional antigen-presenting cells (APC), e.g., monocytes, monocyte-derived cells, macrophages, dendritic cells. In cancer patients, cells of the tumor have been found to express MHC class II molecules (Dengjel et al., 2006).
Elongated (longer) peptides of the invention can act as MHC class II active epitopes.
T-helper cells, activated by MHC class II epitopes, play an important role in orchestrating the effector function of CTLs in anti-tumor immunity. T-helper cell epitopes that trigger a T-helper cell response of the TH1 type support effector functions of CD8-positive killer T cells, which include cytotoxic functions directed against tumor cells displaying tumor-associated peptide/MHC complexes on their cell surfaces. In this way tumor-associated T-helper cell peptide epitopes, alone or in combination with other tumor-associated peptides, can serve as active pharmaceutical ingredients of vaccine compositions that stimulate anti-tumor immune responses.
It was shown in mammalian animal models, e.g., mice, that even in the absence of CD8-positive T lymphocytes, CD4-positive T cells are sufficient for inhibiting manifestation of tumors via inhibition of angiogenesis by secretion of interferon-gamma (IFNγ) (Beatty and Paterson, 2001; Mumberg et al., 1999). There is evidence for CD4 T cells as direct anti-tumor effectors (Braumuller et al., 2013; Tran et al., 2014).
Since the constitutive expression of HLA class II molecules is usually limited to immune cells, the possibility of isolating class II peptides directly from primary tumors was previously not considered possible. However, Dengjel et al. were successful in identifying a number of MHC Class II epitopes directly from tumors (WO 2007/028574, EP 1 760 088 B1).
Since both types of response, CD8 and CD4 dependent, contribute jointly and synergistically to the anti-tumor effect, the identification and characterization of tumor-associated antigens recognized by either CD8+ T cells (ligand: MHC class I molecule+peptide epitope) or by CD4-positive T-helper cells (ligand: MHC class II molecule+peptide epitope) is important in the development of tumor vaccines.
For an MHC class I peptide to trigger (elicit) a cellular immune response, it also must bind to an MHC-molecule. This process is dependent on the allele of the MHC-molecule and specific polymorphisms of the amino acid sequence of the peptide. MHC-class-1-binding peptides are usually 8-12 amino acid residues in length and usually contain two conserved residues (“anchors”) in their sequence that interact with the corresponding binding groove of the MHC-molecule. In this way each MHC allele has a “binding motif” determining which peptides can bind specifically to the binding groove.
In the MHC class I dependent immune reaction, peptides not only have to be able to bind to certain MHC class I molecules expressed by tumor cells, they subsequently also have to be recognized by T cells bearing specific T cell receptors (TCR).
For proteins to be recognized by T-lymphocytes as tumor-specific or -associated antigens, and to be used in a therapy, particular prerequisites must be fulfilled. The antigen should be expressed mainly by tumor cells and not, or in comparably small amounts, by normal healthy tissues. In a preferred embodiment, the peptide should be over-presented by tumor cells as compared to normal healthy tissues. It is furthermore desirable that the respective antigen is not only present in a type of tumor, but also in high concentrations (i.e. copy numbers of the respective peptide per cell). Tumor-specific and tumor-associated antigens are often derived from proteins directly involved in transformation of a normal cell to a tumor cell due to their function, e.g. in cell cycle control or suppression of apoptosis. Additionally, downstream targets of the proteins directly causative for a transformation may be up-regulated and thus may be indirectly tumor-associated. Such indirect tumor-associated antigens may also be targets of a vaccination approach (Singh-Jasuja et al., 2004). It is essential that epitopes are present in the amino acid sequence of the antigen, in order to ensure that such a peptide (“immunogenic peptide”), being derived from a tumor associated antigen, leads to an in vitro or in vivo T-cell-response.
Basically, any peptide able to bind an MHC molecule may function as a T-cell epitope. A prerequisite for the induction of an in vitro or in vivo T-cell-response is the presence of a T cell having a corresponding TCR and the absence of immunological tolerance for this particular epitope.
Therefore, TAAs are a starting point for the development of a T cell based therapy including but not limited to tumor vaccines. The methods for identifying and characterizing the TAAs are usually based on the use of T-cells that can be isolated from patients or healthy subjects, or they are based on the generation of differential transcription profiles or differential peptide expression patterns between tumors and normal tissues. However, the identification of genes over-expressed in tumor tissues or human tumor cell lines, or selectively expressed in such tissues or cell lines, does not provide precise information as to the use of the antigens being transcribed from these genes in an immune therapy. This is because only an individual subpopulation of epitopes of these antigens are suitable for such an application since a T cell with a corresponding TCR has to be present and the immunological tolerance for this particular epitope needs to be absent or minimal. In a very preferred embodiment of the invention it is therefore important to select only those over- or selectively presented peptides against which a functional and/or a proliferating T cell can be found. Such a functional T cell is defined as a T cell, which upon stimulation with a specific antigen can be clonally expanded and is able to execute effector functions (“effector T cell”).
In case of targeting peptide-MHC by specific TCRs (e.g. soluble TCRs) and antibodies or other binding molecules (scaffolds) according to the invention, the immunogenicity of the underlying peptides is secondary. In these cases, the presentation is the determining factor.